The main idea is explained by the important information in the major supporting details. Minor supporting details add to this information and give more information that isn’t necessary for the reader to understand the main idea. There is no hard and fast rule about how many of each type of detail should be in a paragraph.
Major details help the reader understand the topic of the paragraph or text by giving them the basic information they need to know. These can be thought of as the main points of the topic, which the reader can focus on to get the main idea if he doesn’t want to go into more detail. Most paragraphs have at least two or three of these.
Minor details that back up the main idea are more specific and give information that the reader doesn’t need to know. If the reader is not interested in such specifics, they can skip over this information. Smaller details that back up the main points made in the main details and give more information about the topic.
Both big and small details are needed to build up the topic, and the development of the paragraph depends on these details, though the big ones are more important. In general, details that back up the main idea of a paragraph are called “supporting details.”